Styrene resins have good shapability and good mechanical properties, and are inexpensive, therefore, they are widely used. Especially a styrene resin modified with polybutadiene exhibits excellent impact resistance and widely used in home electric appliances. However, a problem arises such that the impact resistance is enhanced but transparency drastically decreases with incorporation of the polybutadiene modifier.
Several proposals have been made to solve the above-mentioned problem. For Example, a method of modifying a styrene resin by incorporating therein a styrene-butadiene block copolymer prepared by using an alkali metal catalyst such as n-butyllithium has been proposed (see, for example, Japanese Unexamined Patent Publication (hereinafter abbreviated to “JP-A”) S63-48317, JP-A H1-172413 and JP-A H5-331349). According to this method, styrene-butadiene rubber panicles dispersed in the styrene resin have a particle diameter smaller than that in the case when the polybutadiene modifier is incorporated, and consequently the rubber particles give a modified resin having an improved transparency.
Another proposal of providing a styrene resin having improved transparency and impact resistance has been made wherein an aromatic vinyl monomer such as styrene, methyl methacrylate and an acrylic acid alkyl ester are graft-copolymerized in the presence of a block copolymer such as a styrene-butadiene block copolymer (sec, for example, JP-A S62-169812).